Oxford , England -LRB- CNN -RRB- -- WikiLeaks.org , the website that released secret video of a U.S. airstrike in Iraq that killed a dozen civilians , is `` getting an enormous quantity of whistle-blower disclosures of high caliber , '' the site 's founder , Julian Assange , said Friday in a rare public appearance here .

Speaking at the TED Global conference , Assange said that `` we are overwhelmed by our growth '' and the site ca n't keep up with the volume of the new material because it does n't have enough people to verify it .

He later told reporters that `` there are many things which are very explosive . ''

Assange said the organization gets material from whistle-blowers in a variety of ways -- including via postal mail -- vets it , releases it to the public and then defends itself against `` the regular political or legal attack . ''

He said the organization rarely knows the identity of the source of the leak . `` If we find out at some stage , we destroy that information as soon as possible , '' he said .

Pfc. Bradley E. Manning , 22 , of Potomac , Maryland , has been charged with eight violations of the U.S. Criminal Code for allegedly illegally transferring classified data , including the video that wound up on WikiLeaks . He has been accused of `` wrongfully introducing a classified video of a military operation filmed at or near Baghdad , Iraq '' around July 12 , 2007 , `` onto his personal computer , a non-secure information system . ''

Assange said at a news conference that Manning `` is a political prisoner being held in the nation of Kuwait , effectively keeping him away from the press and effective legal representation . '' He said WikiLeaks is providing legal assistance to Manning without saying if he was the source of the video .

`` Obviously , we can not pick and choose , '' said Assange , adding that the site has to defend everyone who faces serious charges as a result of material posted on WikiLeaks .

The video shows aerial footage of an attack by a U.S. Apache helicopter that killed civilians , including two journalists from the Reuters news service . WikiLeaks posted it in April . The site said the video `` clearly shows the unprovoked slaying of a wounded Reuters employee and his rescuers . ''

Asked to respond to Assange 's assertion that Manning is a `` political prisoner , '' Pentagon spokesman Col. David Lapan told CNN that Manning is `` accused of committing serious offenses . He has been charged under the Uniform Code of Military Justice and will be processed by normal procedures through the military justice system . ''

U.S. military authorities have warned that the publication of classified documents on WikiLeaks could aid in the planning of terrorist attacks and harm national security .

At the Oxford event , Assange said , `` Remember the people in Baghdad , the people in Iraq , the people in Afghanistan , they do n't need to see the video . They see it every day . '' He said the site 's hope is that such video `` will change the perception of the people who are paying '' for the war .

Assange denied reports that WikiLeaks had received hundreds of thousands of classified U.S. cables in addition to the Iraq video . He said the site would have released the cables if it had received them .

Assange said some information , including a patient 's medical records , should legitimately be kept secret . But he said WikiLeaks 's practice of revealing information from whistle-blowers follows the traditions of journalism . The fact that governments and organizations spend money to keep this information secret , Assange said , is a good indication that releasing the information can achieve reform .

The 39-year-old Assange , who has gray hair swept back behind his ears , noted that WikiLeaks operates in several countries , including Iceland and Sweden , where , he said , laws give protection to the disclosures made on the site . He said he had to cancel three public appearances in the United States , including one at the June conference of Investigative Reporters and Editors in Las Vegas , Nevada , because of `` unreasonable '' statements by U.S. officials in private that they `` may not follow the rule of law '' in dealing with him .

`` I received advice from figures like -LSB- investigative reporter -RSB- Sy Hersh to exercise caution , '' Assange said , adding that U.S. officials have now adopted a `` reasonable '' attitude in private .

Assange was interviewed by Chris Anderson , curator of TED , the nonprofit that ran the conference . He asked the audience for a show of hands as to whether he was a hero or a `` dangerous troublemaker . '' The vast majority signaled that they viewed him as a hero .

CNN 's Mike Mount and Alan Silverleib contributed to this report .

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NEW : Pentagon says Pfc. Bradley E. Manning is accused of `` serious offenses ''

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WikiLeaks founder Julian Assange : Site getting a number of whistle-blower disclosures

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Assange : Manning is a `` political prisoner ''

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Assange says he has canceled U.S. appearances due to security concerns